This invention relates to the construction of an electric furnace in which the furnace wall includes a liner of ceramic insulating material.
Electric furnaces have been provided with a metallic outer shell and a liner of ceramic insulating material, one such furnace construction being shown in U.S. Pat. No. 3,987,237. However, this prior construction requires the use of a liner constructed of a fiberboard or "hardboard" type of insulating material, which type of construction is very expensive. In U.S. Pat. No. 3,705,253, there is shown an electric furnace employing a fibrous insulating material as a liner. However, the means for securing the insulating material onto the wall is unsatisfactory in that it does not hold the insulation material properly and cannot be replaced feasibly.
It is the general object of the invention to provide an electric furnace construction in which the furnace wall is comprised of an outer shell and a liner of a soft ceramic fiber insulating material. There is provided liner holding means comprising novel pin assemblies which simultaneously hold the liner tightly against the shell and provide a mechanical support for the electric heating means.
A feature of the novel pin assembly construction is that it provides mechanical flexibility to accommodate strip or coiled wire type of metallic heating elements of various dimensions. Also, the design permits easy replacement of the pins of the pin assemblies in a minimum of time. It is noted that the pins are arranged to carry the heating elements in a cantilevered or overhung arrangement so that they are subject to occasional breakage and must be replaced. The design of the invention is such that the pins can be replaced with little or no damage to the ceramic fiber material which is weak by reason of its soft fiberlike composition. Furthermore, the pin assemblies are constructed to locate the heating elements so as to be positioned a reasonable distance from the hot face of the ceramic material which arrangement is important in that if the heating element is permitted to come too close to the fiber, localized overheating and premature failure of the heating elements will result.